Robert Pattinson Leighton Meester Dating?

Talk about an unlikely couple! Kristen Stewart’s perma-scowl is gonna be working overtime once she gets wind of reports that Robert Pattinson — her rumored love interest on and off the set of the Twilight films — has been secretly bumping uglies with Gossip Girl star Leighton Meester.

Pattz and Meester, who recently ditched longtime beau Sebastian Stan, have reportedly been sexting each other and hooking up for late night rendezvous at the brunette’s Manhattan bachelorette pad, In Touch Weekly is reporting.

“He ducked out of the building and hopped into a waiting car,” says a spywitness, who spied Rob sneaking out of her . “He apparently spent the night with Leighton, and didn’t want anyone to know! She’s having a texting romance with him, and is so into it. She talks with Rob almost daily.”